A device for transanally introducing an infusion into the rectum of a patient, the device comprising an inflatable balloon having a waisted shape, two terminal sections of larger radius and, a middle section of a reduced radius, and is placed transanally, the distally adjoining radially enlarged balloon section being placed intrarectally and the proximally adjoining radially enlarged balloon section extracorporeally, wherein both balloon ends taper to the dimension of a shaft supporting the balloon and are fixed on the surface of the shaft such that as the balloon is filled, the two enlarged balloon sections move toward each other in opposite axial directions, and wherein the two radially enlarged balloon sections are enlarged relative to the middle balloon section, such that when the balloon is placed transanally, during the filling process the two radially enlarged balloon sections draw down over the middle, balloon section and contact each other, and to a method for filling the catheter balloon.
